As a method for producing (−)-1-(3-hydroxypropyl)-5-[(2R)-2-({2-[2-(2,2,2-trifluoroethoxy)phenoxy]ethyl)}amino)propyl]-2,3-dihydro-1H-indole-7-carboxamide (generic name: silodosin, which may hereinafter be referred to as “compound (1)”), there is known, for example, a method in which: a compound represented by formula (A) and a compound represented by formula (B) are reacted to obtain a compound represented by formula (C) (3-{7-cyano-5-[(2R)-2-({2-[2-(2,2,2-trifluoroethoxy)phenoxy]ethyl}amino)propyl]-2,3-dihydro-1H-indol-1-yl}propyl benzoate); then the benzyl group is removed to produce a compound represented by the formula (D) (7-cyano-1-(3-hydroxypropyl)-5-[(2R)-2-({2-[2-(2,2,2-trifluoroethoxy)phenoxy]ethyl)}amino)propyl]-2,3-dihydro-1H-indole); and further the cyano group is converted into an amide group through hydrolysis to produce the compound (1) (see Patent Literature 1, for example).

In the meantime, three crystal forms, α-crystal, β-crystal, and γ-crystal, are known for the compound (1) (see Patent Literature 3, for example). In particular, Patent Literature 3 discloses that the α-crystal is white and that the α-crystal is beneficial as a crystal for oral solid medicine in terms of hygroscopicity and stability.